71 



endowed with various modes of reproduction employ these 

 differently under differing external conditions i regard as an in- 

 disputable fact, which in my opinion has hardly been appreciated 

 by zoologists, whilst to botanists, whose knowledge of the life- 

 conditions and vital requirements of plants exceeds by far that of 

 zoologists with regard to animals it has long been an acknow- 

 ledged fact. In botanical literature it has often been emphasized, 

 that sexual reproduction is abandoned in high latitudes, and 

 that plants living under arctic conditions increase either chiefly 

 or exclusively vegetatively. To mention an example Nathorst 

 (1883 p. 64) reports that a great many of the Spitzbergen plants 

 produce no fruit at all; the phenomenon is even observable 

 in the Færoe Islands (Ostenfeld 1901 p. 106 and 1906 p. 41 

 where further literature is cited). In botany it is so pronounced, 

 that plants which in a given locality do not produce ripe seeds 

 are considered by some botanists as relicts, a view which how- 

 ever can hardly be supported (Warming 1904 p. 74). With 

 regard to plants fertilized by the aid of insects it is of course 

 often the absence of the proper insects which forms a hindrance 

 in this respect. Ostenfeld further remarks, that with regard 

 to wind fertilized plants the explanation of the above feature 

 must be sought for in climatic conditions, more especially the 

 low summer temperature — the same interpretation as has been 

 propounded in recent zoological literature on the various modes 

 of propagation of the lower fresh -water organisms in high 

 northern latitudes. 



1 shall not here enter upon this now pretty extensive 

 literature, comprising numbers of greatly differing organisms, 

 but only restrict myself to a few remarks respecting the 

 Bryozoa. 



Already in 1896 (p. 350) I was of opinion, that the sexual 

 reproduction of the Bryozoa decreases towards the north. Not- 

 withstanding regular fortnightly investigations made upon colonies 

 of P. fruticosa, Fredericella and Lophopus in their habitual 



